1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image on paper.
2. Description of the Related Art
Individual sections of a color copier or printer have hitherto been optimized for attaining the best picture quality on specialized paper. For this reason, satisfactory picture quality can be attained at the time of use of specialized paper. However, in many cases satisfactory picture quality cannot be attained through use of paper other than specialized paper, such as plain paper or recycled paper. Particularly, when an image is formed on foreign-made coarse paper, inconsistencies in picture quality arise, whereas minimum inconsistencies in picture quality arise when an image is formed on specialized paper. The degree of inconsistency in picture quality becomes more noticeable in the following sequence: Japanese-made plain paper, Japanese-made recycled paper, and foreign-made plain paper.
For instance, in a case where an electrophotographic method is used as an image formation method, random inconsistencies (such as inconsistencies in gloss or fixing inconsistencies) arise in an image for reasons of inconsistencies in the fineness of paper when toner is fixed on paper. The random inconsistencies become more noticeable in a halftone area than in a solid-toned area having a high pile height.
A conceivable method of improving inconsistencies is described in, for example, Japanese Patent Application Laid-Open No. 104754/1993. In an ink-jet recording method for squirting ink by means of an electric field, picture quality is improved by means of changing an applied voltage, to thereby control ink dots at the time of formation of an image on paper having a low degree of smoothness. In a real situation, however, picture quality is not improved, for reasons of smearing.
Japanese Patent Application Laid-Open NO. 55085/1998 describes an electrophotographic method, wherein an image is smoothed through use of transparent toner, thereby attaining high picture quality. However, use of transparent toner adds to the cost of an ordinary office printer and operating costs thereof. Thus, the method is not acceptable.
Japanese Patent Application Laid-Open No. 69960/1997 describes a method in which color transformation operation is performed according to the type of paper, such as plain paper or woodfree paper, thereby improving color reproduction. According to this invention, the type of paper is identified by means of an identification mark affixed on paper, surface reflectivity, or surface roughness. The surface reflectivity of paper indicates the brightness of paper. Similarly, according to a method described in, for example, Japanese Patent Application Laid-Open No. 39223/1992, the reflectivity of paper is determined by the steps of: radiating light onto paper, and measuring light reflected from the paper through use of a sensor, to thereby determine the degree of brightness.
Thus, attention has hitherto been paid to the characteristics of paper, such as brightness and smoothness (i.e., surface roughness), to thereby identify the type of paper. An image is formed in a manner corresponding to the type of paper. Even in a case where image production parameters are changed according to the type of paper, the previously-described inconsistencies sometimes arise even when paper of the same type is used for printing.
The present invention has been conceived in view of the drawbacks of the background art and is aimed at providing an image forming apparatus capable of forming an inconsistency-free image of good picture quality.
According to the present invention, there is provided an image forming apparatus characterized in that an image is formed on paper by means of setting parameters to image formation means according to the formation of paper on which an image is to be formed. As used herein, xe2x80x9cformation of paper relates to the composition and texture of paper.xe2x80x9d As has been mentioned previously, brightness or smoothness has hitherto been used as a typical characteristic value of paper pertaining to picture quality. Subjective evaluation of the relationship between brightness, smoothness, and picture quality has been tested. Test results are converted into numerals; that is, sensory scores, and the coefficients of correlation are determined from the sensor scores. The coefficient of correlation between brightness and picture quality assumes a value of 0.53. The coefficient of correlation between smoothness and picture quality assumes a value of 0.59. Similarly, the coefficient of correlation between a formation index indicating the formation of paper and picture quality was determined through a test. The coefficient of correlation between formation and picture quality assumes a value of 0.80. It can be said that the correlation between formation and picture quality is most strong. For this reason, the present invention pays attention, as a characteristic factor of paper, to formation having a high correlation with picture quality. Parameters are set in accordance with a formation index. As a result, inconsistencies appearing in a formed image are diminished, thereby improving picture quality.
As examples of the parameters to be set in accordance with the formation of paper, there can be set: for example, a color correction parameter to be used for a color correction operation; a parameter for controlling the amount of black coloring material at the time of removal of base color and at the time of production of a black plate; a spatial filtering operation parameter; a xcex3 correction operation parameter; and a parameter for instructing the number of screens used for screen processing or a growth pattern. In a case where an image is formed through use of the electrophotographic method, parameters for controlling voltages used for electrification, exposure, and development, a parameter for controlling a voltage or current to be used for transfer of an image, and a parameter for controlling temperatures or pressure at the time of an fixing operation can be set in accordance with the formation of paper.
An image forming apparatus can be configured so that a user can set the formation of paper from operation means or remotely by way of external interface means. Alternatively, the formation of paper can be automatically detected through use of sensor means.